The synthesis, as well as the chemical, electrical and photoelectrical characteristics of nonpolymeric and polymeric organic semiconductors and conductors have formed the subject of intense research. The state of present knowledge, as well as the in part differing opinions have been discussed in numerous works, cf G. Wegner, Angew. Chem. Vol. 93, pp. 352 to 371, 1981; M. Hanack, Naturwiss, Vol. 69, pp. 266 to 275, 1982; A. Heeger et al, Synthetic metals, Vol. 6, pp. 243 to 263, 1983; and K. Seeger, Angew. Makromol. Chem., Vol. 109/110, pp. 227 to 251, 1982.
The term "conductive polymers" is understood to mean polyconjugate systems, such as occur in polyacetylene (PAc), poly-1,3,5 . . . n-substituted polyacetylenes, acetylene copolymers, as well as 1,3-tetramethylene-bridged polyenes, e.g. polymers resulting from the polymerization of 1,6-heptadiene and similar polyacetylene derivatives. It also includes the various modifications of polyparaphenylenes (PPP), the different modifications of polypyrroles (PPy), the different modifications of polyphthalocyanines (PPhc) and other polymeric conductors, such as polyanilines, polyperinaphthalines etc. They can be present as such or as polymers complexed ("doped") with oxidizing or reducing substances. Complexing generally leads to an increase in the electrical conductivity by several decimal powers and into the metallic range.
The term "organic conductors" is understood to mean nonpolymeric, organic substances, particularly complex salts or charge transfer complexes, e.g. the different modifications of tetracyanoquinodimethane (TCNQ) salts.
Conductive polymers are in part obtained as polycrystalline powders, film-like agglomerates or lumps of primary particles. As e.g. polyacetylene is neither soluble nor fusible, it constituted an important advance when Shirakawa was able to produce self-supporting, but very thin films by interfacial polymerization, whose characteristics are similar to those of thin polymer films. Tests carried out on these films concerning the morphology of polyacetylene led to a fibril theory, according to which the polyacetylene is assembled to give elongated fibres through which crystalline regions form in the fibre direction, in which the current flows along the fibre axis following doping (complexing).
The general opinion is that the conductivity is brought about by the high crystallinity and by the arrangement of the polyconjugate systems (optionally in complexed form). However, it has not as yet been adequately clarified whether the conductivity mechanism in polyenes and polyphenylenes, as well as polypyrroles is determined by electron transfers along the chain or at right angles to the chain direction, particularly as the morphology of conductive polymers has also not yet been clarified. In this connection, the inventor has proved that the primary particles of polyacetylene are always extremely fine spherical particles, which in part agglomerate to fibrillar secondary particles and in part agglomerate to non-directed foil-like film, cf B. Wessling, Makromol. Chem., Vol. 185, 1265-1275, 1984. By reference the contents of this paper form part of the disclosure of the present description.
The literature provides the following information concerning the physical characteristics and processability of conductive polymers and organic conductors:
High crystallinity, e.g. polycrystalline powders, in individual cases long needle-shaped crystals (for TCNQ, cf Hanack, 1982), or other macroscopic crystal shapes, e.g. in the case of polyphthalocyanines. In the case of polyacetylene, the size of the crystallites clearly does not exceed 100 .ANG. (D. White et al, Polymer, Vol. 24, p. 805, 1983).
Polyconjugate polymers, are, in their basic state, insulators, as opposed to polymer-bridged charge transfer complexes, such as polyphthalocyanines (cf Hanack, loc. cit, pp. 269/270).
Optical appearance generally matt black (glossy or shining only if the synthesis was carried out on the smooth surfaces, cf the Shirakawa method for producing self-supporting "films", in which the side facing the glass is glossy and that remote from the glass matt). Polyphthalocyanines are non-glossy powders, which appear blue.
If, as a result of the synthesis conditions, macroscopically larger structures can be obtained, they are brittle (the exception being cis-polyacetylene). Due to their crystalline structure, charge transfer complexes are always very brittle substances, which are very difficult to process mechanically (Hanack, loc. cit, pp. 269/270). Much the same applies for uncomplexed and particularly complexed conductive polymers.
Conductive polymers and organic conductors are generally insoluble, infusible and not shapable, whilst in most cases being unstable relative to oxygen, moisture and elevated temperatures. If e.g. in the case of nonpolymeric or polymeric charge transfer complexes (TCNQ or PPhc), melting points can in fact be observed, they are close to the decomposition point, so that decomposition-free melting is either impossible or is only possible with great difficulty. To the extent that soluble derivatives exist in the case of the different conductive polymers, their conductivity is several decimal powers inferior compared with the insoluble non-modified substances. A thermoplastic deformation of conductive polymers and organic conductors has not as yet proved possible. Polypyrrole and certain representatives of the polyphthalocyanines are comparatively stable with respect to oxidative and thermal influences, cf Hanack, loc. cit; K. Kanazawa et al, J. Chem. Soc., Chem. Comm. 1979, pp. 854/855.
Hanack's 1982 statement that most organic conductors and conductive polymers were primarily produced under the standpoint of high conductivity, whilst ignoring their mechanical properties, stability and processability, still applies. The following statements are made regarding the physical characteristics of organic conductors and conductive polymers which are important for processability.